1. Field of the Invention
The invention relates to the art of optical fiber splicing. More particularly, the invention pertains to methods of splicing optical fibers with other optical fibers or optical waveguides. The invention further provides optical fiber splicing elements useful for coupling optical fibers and for alignment of optical fibers with waveguides. The splicing elements allow for accurate lateral and longitudinal alignment and improved collinearity of spliced optical fibers, achieving low coupling loss.
2. Description of the Related Art
Recent developments in the area of optical communications have provided a large number of devices for the control and routing of light. These devices can be characterized as passive devices, those which serve only to route the propagation of light along a particular path, and active devices, those which control some function of the propagating light, such as its intensity or polarization, or which dynamically control the path along which the light propagates. Optical fibers have been the medium of choice in the field of optical communications for long distance propagation of light due to their excellent transmission characteristics and ability to be fabricated in lengths of many kilometers.
Light propagates through the core region of optical fibers and these core regions can be as small as a few microns in diameter. At some point multiple optical fibers must be joined together, and the more compact and less loss-inducing the connection can be, the better.
Accordingly, the accurate alignment of fibers is critical to preclude wasting a substantial amount of light through the coupling. Further, as optical devices continue to shrink, and integration of multiple devices on a single chip becomes more popular, planar fiber positioning elements become more valuable. Numerous articles and methods have been devised in the prior art to provide planar fiber positioning elements which allow for efficient coupling of optical fibers to substrates. The need for critical alignment tolerances has resulted in a high degree of complexity and cost for these devices and methods of the prior art.
There are many descriptions of methods which utilize silicon "V-grooves" as fiber positioning elements. U.S. Pat. No. 4,767,174 makes use of the fact that certain crystalline orientations of silicon substrates can be preferentially etched to a high degree of accuracy. This is accomplished by a series of lithographic steps including resist coating and exposure, followed by liquid etching. However, once the V-groove is fabricated, it serves only to position the optical fiber relative to the surface of the silicon substrate. It still remains to position the fiber end relative to the end of any other features on the substrate, such as optical waveguides. This is usually accomplished by micromanipulation of the two components relative to each other followed by fixing the alignment by an optical quality glue. Micromanipulation is an expensive and time consuming operation for use in a manufacturing operation.
Alternatively, the V-groove and optical fiber can be positioned relative to a waveguide by the use of additional positioning elements, but these also increase the complexity and cost of the method. Even when the V-groove technique is utilized only to couple two optical fibers to one another, as in U.S. Pat. No. 4,973,126, there are several additional positioning elements required. Also, the V-groove techniques serve to position an optical fiber relative to some surface, such as that of the silicon itself, but the V-groove does not provide any force to retain the optical fiber in position. That is, the optical fiber can easily slip out of the groove unless one or more additional elements are present to provide some retaining force. Typically, a cover plate or a second substrate containing V-grooves is forced down in contact with the optical fibers to hold them in the V-grooves and an optical cement or photopolymer is used to hold the assembly together.
U.S. Pat. No. 4,735,677 describes a method for providing guides for aligning optical fibers on the surface of a silicon substrate. In this method it is necessary to first grow a layer of glass on the silicon wafer by a soot process wherein a glass precursor is treated by flame hydrolysis to deposit glass particles on the silicon, followed by heating in an electric furnace to consolidate the glass. This layer of glass is then lithographically patterned and etched, as by reactive ion etching (RIE), to form the positioning elements. After formation of these elements, an optical fiber can be inserted between them and fixing is accomplished with an adhesive or by melting the glass with a CO.sub.2 laser beam. This technique involves a great number of processing steps and is limited to substrates which are not damaged by high temperature processes or those which do not contain sensitive electronic devices which would be damaged by an RIE etch. Further, like the V-groove techniques, it serves only to position the optical fibers yet provides no rigidity or retaining force to the coupling except through the addition of an adhesive or another high temperature melting process.
U.S. Pat. No. 4,796,975 teaches a method of aligning and attaching optical fibers to substrate optical waveguides. One or more slabs of preferentially etchable material and a waveguide substrate are placed adjacent to each other face down on a flat surface for aligning the tops of the slabs with the top of the waveguide. A backing plate is secured to the back surface to hold the entire assembly together. The preferentially etchable material is thereafter etched to form V-grooves in alignment with the light guiding region of the waveguide substrate. Thereafter, optical fibers are secured thereto in an optically aligned manner with the light guiding region. In another aspect, the invention is directed to a fiber pigtailed waveguide substrate manufactured in accordance with the method.
U.S. Pat. No. 4,750,799 teaches a hybrid optical integrated circuit having a high-silica glass optical waveguide formed on a silicon substrate, an optical fiber and an optical device coupled optically to the optical waveguide, and an optical fiber guide and an optical device guide on the substrate for aligning the optical fiber and the optical device at predetermining positions, respectively, relative to the optical waveguide. Islands carrying electrical conductors are disposed on the substrate, a first electrical conductor film is formed on the substrate, second electrical conductor films are formed on the top surfaces of the optical waveguide, the optical fiber guide, the optical device guide and the islands and are electrically isolated from the first electrical conductor film.
U.S. Pat. No. 5,359,687 teaches an optical coupling device comprising a substrate having a surface region at a pre-determined position on a surface of said substrate for placement of an optical waveguide, a channel on the surface of the substrate for optically aligning and coupling an optical fiber and an optical waveguide positioned at the predetermined position, wherein the longitudinal axis of the channel is in alignment with the predetermined position such that on placement of the optical fiber in the channel and placement of the optical waveguide in the position the light carrying core of the fiber and the waveguide are substantially in optical alignment.
None of these prior disclosures teach the ability to precisely and accurately position fibers on almost any flat substrate, while taking up very little space. The object of the present invention provides a secure retaining force to the optical fiber without the need for additional elements held in place by optical adhesives or thermal heat treatments and requires no complex manufacturing steps or elaborate alignment by a micromanipulator. The invention provides strips of polymeric splice elements, also known as elastomeric polymer grippers, to provide a splice means for optical fibers. Once these grippers are deposited on a substrate, optical fibers can be snapped between them and positioned in close contact to minimize loss of propagation. Also, through adjustment of the length of the grippers and their separation distance, lateral and longitudinal alignment, and collinearity are easily controlled.